The present invention relates to a composite magnetic material more particularly usable as a microwave absorbing material in the longwave range between 50 MHz and a few GHz.
In the application to microwave absorption, the composite material according to the invention can be particularly used as a coating material or an anechoid or echo-free chamber and as an electromagnetic filter more particularly used in telecommunications, data processing and microwave ovens.
The presently known microwave absorbing materials are in the form of thin films, with a thickness below a few cm, made from dense materials such as ferrite, or from the dispersion of these dense materials in an appropriate organic binder.
In particular, ferrite tiles are commercially available which absorb microwaves between 100 and 1000 MHz, have a thickness of 5 to 15 mm and a high surface density of approximately 20 to 30 kg/m.sup.2. There are also charged or filled organic composite materials, such as rubbers charged with ferrites or metals, whose use frequency varies from 5 to 15 GHz, whose thickness varies from 1 to 5 mm and whose high surface density varies from 2 to 15 kg/m.sup.2.
Other known microwave absorbing materials are pyramidal structures or alveolar structures having a thickness of several dozen centimeters and a limited surface density between 1 and 5 kg/m.sup.2. The latter materials are generally used for equipping echofree chambers for experimental research.
No matter what the nature and application of the known microwave absorbing materials, the weight problem arises. Either the products are thin but dense, or are light but thick. These weight and overall dimensional problems considerably limit the applications of these absorbing materials, each structure or configuration being specific to a particular application. Moreover, their microwave absorption is generally limited to a small wavelength range.